A magnetic disk drive has a rotatable magnetic disk, a magnetic head slider supported by a suspension and carrying read/write elements thereon, and a positioning mechanism for moving and positioning the magnetic head slider in a radial direction of the magnetic disk through the suspension, the magnetic head slider being adapted to travel over the magnetic disk relatively to read and write information with respect to the magnetic disk. The magnetic head slider flies stably over the magnetic disk through an air bearing. In order to attain a high recording density of the magnetic disk drive and a consequent larger capacity of the magnetic disk drive, it is necessary to shorten the distance between the magnetic head slider and the magnetic disk, that is, shorten the flying height of the slider, thereby increasing a linear recording density.
In designing a flying height of a slider heretofore, allowance is made for a decrease of the flying height caused by, for example, variations in machining, a temperature difference between working environments or a difference between a flying height in write mode and that in read mode, and a flying height margin is provided to avoid slider-disk contact even in the worst condition. However, with use of a slider having a function of adjusting the flying height head by head or in accordance with a working environment, it is possible to get rid of the above flying height margin and greatly reduce the slider flying height while avoiding slider-disk contact. Recently, the slider flying height has been reduced to about 10 nm or less.
Japanese Patent Publication No. 2005-135501 (“Patent Literature 1”) has proposed a slider structure wherein a heater formed by a thin film resistor is disposed near both read and write elements and a part of a slider is heated as necessary and is thereby thermally expanded and projected to adjust the distance between the read/write elements and a magnetic disk. Japanese Patent Publication No. 2005-056447 (“Patent Literature 2”) has proposed a slider structure wherein a heater is disposed away from the tips of read/write elements and both heater and read/write elements are enclosed with a resin film of low rigidity, thereby increasing the amount of projection of the read/write elements per unit electric power without raising the temperature of the read element which weaken against a thermal load.
As noted above, by using the flying height adjusting type magnetic head slider which utilizes thermal expansion and projection with a heater, it becomes possible to correct variations in machining, variations in flying height caused by a temperature difference between working environments and a difference between a flying height in write mode and that in read mode. However, it had been found that if a heater is disposed near such a read element as a GMR head or a TMR head, an induction field generated by an electric current flowing in a heater coil exerts an influence on the magnetization of a magnetic shield of the GMR head or the TMR head.
FIG. 7 shows a sectional structure of the magnetic head slider described in Patent Literature 1 and the layout of a lower magnetic shield and a heater coil. In the illustrated structure, a magnetic head slider 1000 has a heater 400, a read element 200 and a write element 300 which are stacked on an element forming surface of a slider substrate 110. The read element 200 has a lower magnetic shield 210, a GMR film or a TMR film 220 and an upper magnetic shield 230. The heater 400 is formed by causing a thin film resistance wire (heater coil) 410 to meander in a track width direction X below the lower magnetic shield 210. In FIG. 7, in order to make the meandering direction of the heater coil 410 easier to see, the heater coil 410 is shown schematically on the lower magnetic shield 210. When an electric current i is supplied to the heater coil 410, induction fields are generated in both hx and hy directions. Magnetic fields generated in the track width direction X of the lower magnetic shield 210 are offset each other, but a magnetic field hy generated in a direction (ABS direction) orthogonal to the track width direction extends into the lower magnetic shield 210.
The upper and lower magnetic shields 230, 210 are magnetized uniformly in the track width direction X lest a magnetic noise should be superimposed on a read output of the GMR film or the TMR film 220 disposed between both magnetic shields. However, as noted above, if the induction field by in the ABS direction Y generated by the electric current i flowing in the heater coil 410 extends into the lower magnetic field 210, the magnetizing direction of the lower magnetic field rotates partially and an area is created wherein the magnetization is not uniform. Once such an area of non-uniform magnetization is created in the lower magnetic shield 210, the motion of the magnetic field against an external magnetic field becomes non-uniform and disturbance occurs there. This appears as noise in the read output of the GMR film or the TMR film 220. In particular, in the TMR head, this influence is greater than in the GMR head because it uses both the magnetic shield and the electrode in combination.